REG - Great Southrn.Copper - Drilling Extends Mineralisation at Cerro Negro

Great Southern CopperAnnouncement

Thu 07:10

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RNS Number : 1749L  Great Southern Copper PLC  11 December 2025

 

THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION AS STIPULATED UNDER THE UK
VERSION OF THE MARKET ABUSE REGULATION NO 596/2014 WHICH IS PART OF ENGLISH
LAW BY VIRTUE OF THE EUROPEAN (WITHDRAWAL) ACT 2018, AS AMENDED.  ON
PUBLICATION OF THIS ANNOUNCEMENT VIA A REGULATORY INFORMATION SERVICE, THIS
INFORMATION IS CONSIDERED TO BE IN THE PUBLIC DOMAIN.

 

 

11(th) December 2025

 

Great Southern Copper plc

("GSC" or the "Company")

 

Phase III Drilling Extends High-Grade Cu-Ag Mineralisation at Cerro Negro

With Assay Grades Up to 9.76 % Cu and 778 g/t Ag

 

New sulphide lenses extend potential of the Mostaza system

 

Great Southern Copper plc (LSE: GSCU), the company focused on
copper-gold-silver exploration in Chile, is pleased to provide a progress
update for its Phase III drilling campaign at Cerro Negro, including reporting
of assay results for the first three drill holes.

 

Highlights:

·    Phase III drilling discovers new chalcocite-rich lenses within the
Mostaza Lens 2 zone, indicating potential for a "stacked" system and expanding
the potential scale of the Mostaza deposit

·      First assay results from Phase III drilling at Lens 2 report
significant mineralised intervals including;

o  DD029: 0.69m @ 9.76% Cu and 716 g/t Ag from 87.93 m, within a broader
interval of;

§ 6.32m @ 1.39% Cu and 98.2 g/t Ag from 82.3m

o  DD031: 1.78m @ 4.02% Cu and 271 g/t Ag from 90.4m, and

§ 1.1m @ 8.92% Cu and 715.3 g/t Ag from 96.5m, within a broader interval of;

§ 7.2m @ 2.58% Cu and 188.7 g/t Ag from 90.4m, and

§ 2.15m @ 2.45% Cu and 189.4 g/t Ag from 110.9m

·      New base metal lens with highly anomalous silver-lead-zinc also
discovered in the Mostaza Lens 2 zone

·    Within the Lens 3 - 5 zone, DD026 and DD030 confirm continuation of
the mineralised trend southward, with lens-style alteration and mineralisation
consistent with extensions of the Mostaza system:

o  DD026: 0.77m @ 2.23% Cu and 92.5 g/t Ag from 29.93m

§ And 0.74m @ 1.98% Cu and 94.1 g/t Ag from 66.1m

§ And 0.5m @ 1.09% Cu and 6.4 g/t Ag from 41m

§ And 1m @ 0.91% Cu and 26 g/t Ag from 38m

·      Visual oxide and sulphide mineralisation intersected in scout
reverse circulation ("RC") drilling one kilometre ("km") along trend south of
Mostaza, indicating strong continuity of the system along the Mostaza Fault
Zone; assays pending

·    Approximately 3,000m of Phase III diamond drilling ("DD") and RC
drilling completed, with further assay results pending

·     Petrography confirms Mostaza as high-level epithermal system and
identifies copper-mineralised hydrothermal silica clasts within the
mineralised lens breccias, indicating earlier hydrothermal events and
reinforcing potential for additional mineralisation at depth

·    Metallurgy studies are on-going with seven composite drill samples
delivered to Aminpro Chile SpA for first-pass metallurgical test-work

·      GSC holds option to own 100% of the Cerro Negro prospect,
including the Mostaza mine

·      Prospect located at low elevation with excellent access to
infrastructure and mining services

 

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "Phase
III drilling at Mostaza continues to deliver exciting high-grade copper-silver
results demonstrating the strength and continuity of the copper-silver system
at Cerro Negro. Significantly, the recent drilling at Mostaza has successfully
extended high-grade mineralisation both along strike and down plunge, with the
discovery of new mineralised lenses suggesting a multiple stacked lens
architecture to the system - a feature that materially enhances the potential
scale of the deposit.

 

"The new petrography analysis provides further confidence in the system's
strength, demonstrating that the mineralised breccias at Cerro Negro contain
fragments of earlier copper-mineralised hydrothermal silica, pointing to
multiple mineralising events and the potential for further mineralisation at
depth.

 

"We are also encouraged to see further evidence of the southern continuation
of the mineralised trend in the Lens 3 to Lens 5 areas. Even where copper has
been leached near surface, the style of alteration and silver anomalism is
consistent with the presence of sulphide-rich mineralisation at depth, as we
have observed elsewhere along the trend.

 

"With approximately 3,000 metres of drilling now completed and additional
assays pending, Phase III continues to build momentum. Our technical
understanding of the system is improving rapidly, and these results give us
increasing confidence in the growing potential of the broader Cerro Negro
mineralised trend."

 

 

Phase III Drilling:

 

Approximately 3,000 metres of diamond and RC drilling has now been completed
for the Phase III programme at Cerro Negro. The Company has received the first
assay results from the programme, including complete results for drillholes
CNG25-DD026 and DD029-DD031, with assays from the remaining holes pending.

The Phase III programme has been designed to continue advancing the high-grade
copper-silver discovery at Mostaza by:

·     Infill and step-out drilling at the Mostaza deposit (Lens 2 and
adjacent lenses) to refine the geometry and continuity of the high-grade Cu-Ag
mineralisation

·      Testing extensions of known mineralisation at nearby targets,
including Lenses 3, 4 and 5, where previous drilling intersected strongly
silicified but copper-leached lens rocks indicative of underlying sulphide
mineralisation

·     First-pass scout RC drill testing of geochemical and geophysical
anomalies along the Mostaza Fault Zone to the south of the Mostaza mine

 

 

Figure 1: Cerro Negro Project. Plan view showing drillhole locations and
targets. Drillholes reported in this announcement are labelled.

 

Mostaza Lens 2 (CNG25-DD029 and DD031):

 

Drillhole CNG25-DD031 was drilled as a 25m down-plunge step-out from
CNG25-DD016, which previously intersected 6.7m @ 4.96% Cu and 7.5m @ 4.48% Cu
and 342.6 g/t Ag from 89m¹. DD031 successfully extended the high-grade zone,
intersecting a broad interval of mineralised lens rock including narrower
high-grade Cu-Ag zones including:

 

·      7.2m @ 2.58% Cu and 188.7 g/t Ag from 90.4m, including;

o  1.78 m @ 4.02% Cu and 271 g/t Ag from 90.4 m, and

o  1.1m @ 8.92% Cu and 715.3 g/t Ag from 96.5m

 

This interval contains peak assays of 9.46% Cu and 778 g/t Ag. Antimony is
also notably anomalous with grades up to 0.15% Sb.

 

In addition, DD031 intersected a second, deeper mineralised lens returning
2.15m @ 2.45% Cu, 189.4 g/t Ag and 0.14% Sb from 110.9m, indicating the
potential presence of multiple "stacked" mineralised bodies at depth and
confirming down-plunge continuity.

 

In addition, a shallow, 10m thick upper lens was also intersected in DD031 at
49m down-hole depth, characterised by intense silicification and abundant
pyrite, galena and sphalerite mineralisation, with highly anomalous lead
("pb"), zinc ("zn") and silver up to 0.47% Pb and 0.67% Zn. Based on previous
drilling and surface mapping, this shallow horizon is interpreted as a
possible distal expression of a mineralised lens that may grade into
higher-grade Cu-Ag mineralisation down-dip or along strike.

 

Drillhole CNG25-DD029 was drilled as a 30m along-strike step out to the south
of CNG25-DD015, which previously intersected 9.9m of 5.47% Cu and 442.5g/t Ag
from 41.15m(1). DD029 extended the high-grade zone, intersecting intensely
clay-altered lens rock containing veinlet and disseminated chalcocite with
locally very high-grade:

 

·      6.32m @ 1.39% Cu and 98.2 g/t Ag from 82.3m, including:

o  0.69m @ 9.76% Cu and 716 g/t Ag from 87.93m

 

Together, the results from DD029 and DD031 extend the high-grade
mineralisation both down-plunge and along strike, confirming continuity of the
Cu-Ag system and delivering further high-grade intervals within the central
zone. Significantly, the discovery of additional new mineralised lenses in
DD031 represents a significant development, demonstrating that the system is
not confined to a single horizon but instead comprises a series of repeated,
structurally-controlled, "stacked" sulphide lenses. This thesis is further
supported by subsequent drilling (DD033, 036 and 037, assays pending) and the
emerging geometry materially enhances the potential scale of the Mostaza
deposit and provides clear vectors for ongoing drilling.

Figure 2: Interpreted cross-section, Mostaza Deposit, Cerro Negro Project.
Intervals are reported as down-hole widths

 

 

 

 

 

 

 

Lens 2 extension (DD026):

 

Drillhole CNG25-DD026, located approximately 300m south along trend of Lens 2,
was drilled as a 40m along-strike step-out from CNG25-DD007, which intersected
33 m @ 1.96% Cu and 60.6 g/t Ag from 87 m². DD026 successfully confirmed that
the mineralised lens system persists southwards, intersecting the same
characteristic silica-altered, sulphide-bearing lens rock
(pyrite-chalcopyrite-bornite). Significant intersections include:

·      DD026: 0.77m @ 2.23% Cu and 92.5 g/t Ag from 29.93m

o  And 0.74m @ 1.98% Cu and 94.1 g/t Ag from 66.1m

o  And 0.5m @ 1.09% Cu and 6.4 g/t Ag from 41m

o  And 1m @ 0.91% Cu and 26 g/t Ag from 38m

 

Although the mineralised intervals are narrower than those encountered in
DD007, the presence of multiple sulphide-bearing lenses at shallow depths
provides an important vector for ongoing targeting. The style of alteration
and mineralisation observed in DD026 is consistent with the broader Mostaza
trend and supports the interpretation that higher-grade, thicker Cu-Ag lenses
may develop down-dip or further along strike in this area. These results help
refine the geological model and guide follow-up drilling aimed at identifying
potential thickening or stacking of mineralised bodies.

 

Lens 4 (DD030):

 

Drillhole CNG25-DD030, located approximately 400 m south of Mostaza in the
Lens 4 area, was drilled to test beneath the mapped Lens 4 outcrop and lies
roughly 100 m south along strike of DD014. The hole intersected a shallow
silicified lens zone returning 2.15 m @ 10.2 g/t Ag from 35.2m, consistent
with the elevated silver and strong silica-clay alteration observed in earlier
drilling beneath Lens 4(3).

 

Although copper grades are subdued, the silver-enriched, strongly leached
nature of the interval is characteristic of the near-surface oxidation profile
seen elsewhere at Lens 4 and is interpreted to represent the upper, oxidised
portion of a mineralised lens. Previous drilling in this area (e.g., DD012 and
DD014(3)) shows that copper-rich sulphide mineralisation can develop abruptly
beneath similar leached horizons, and DD030 adds support to this model.

 

These results reinforce the interpretation that mineralisation continues
southwards along the Mostaza structural trend, with the potential for
higher-grade Cu-Ag lenses to occur at depth or along strike. Ongoing
geological and geochemical integration is being used to refine targeting of
the next round of deeper drilling in the Lens 4 corridor.

 

Scout RC drilling - Mostaza Fault Zone:

 

Scout RC drilling continues to test the broader Mostaza Trend, with the RC rig
currently drilling one km south of Mostaza targeting outcropping silicified
lens rock with anomalous Ag+Cu geochemistry at surface. Three drillholes have
been completed to date, and intercepted intervals of silicified breccia
containing visible pyrite, bornite, chalcocite and galena mineralisation(4).
These results indicate that the mineralised system continues along the
southern corridor, and assays are pending.

 

 

 

 

 

Figure 3: Plan map showing exploration drilling results, Cerro Negro Project

Petrographical and Metallurgical Studies:

 

Recent petrographic analysis of select drill core samples from Cerro Negro
confirms that the structurally-controlled, high-grade Cu-Ag mineralisation is
consistent with a low to intermediate sulphidation epithermal type system.
Significantly, the work has also identified that the polymict hydrothermal
breccias that host the Cu-Ag mineralistion also incorporate clasts (fragments)
of copper-mineralised hydrothermal silica and silica-cemented breccias. These
"exotic" hydrothermal quartz clasts are interpreted to represent sampling of
earlier hydrothermal systems, predating the currently recognised Cu-Ag
epithermal mineralisation. This observation supports a model of multiple
mineralising events and suggests the potential for additional, possibly
stronger mineralisation at depth.

 

Metallurgical testwork is ongoing, with 62 samples collected from chalcocite
mineralised zones from five drill-holes of the Lens 2 mineralisation which are
combined into seven representative composite samples of high, medium and low
grade Cu-Ag mineralisation. The samples have been sent to Aminpro Chile SpA in
Santiago for metallurgical analysis. Results are pending.

 

 

References:

1.     RNS  1375O (24(th) June 2025): Exceptional Drilling Results
Continue at Mostaza

2.     RNS 8896D (7(th) April 2025): Further Exceptional Assay Results
from Mostaza

3.     RNS 5588M (12(th) June 2025): Cerro Negro Drilling Confirm
Outstanding Grades

4.     Cautionary note

 

 

Cautionary Note:

Photographs and descriptions of un-assayed drill core and drill chips used in
this RNS are for reference purposes only to describe the style of
mineralisation encountered in the drill hole and do not provide information as
to the metal grade of the rock where that rock has not yet been sampled and/or
assayed. Readers are cautioned not to interpret metal grades or mineralisation
widths from photographs of core or visual descriptions where no corresponding
assays are reported or yet available.

 

 

 

Enquiries:

 Great Southern Copper plc
 Sam Garrett, Chief Executive Officer  +44 (0)20 4582 3500

 SI Capital Limited
 Nick Emerson                          +44 (0)14 8341 3500

 BlytheRay
 Tim Blythe / Megan Ray                +44 (0) 20 7138 3204

                                       gsc@blytheray.com (mailto:gsc@blytheray.com)

 

 

Notes for Editors:

 

About Great Southern Copper

 

Great Southern Copper PLC is a UK-listed mineral exploration company focused
on the discovery of copper-gold deposits in Chile. The Company has the option
to acquire 100% rights to multiple prospects in the under-explored coastal
belt of Chile that are prospective for large scale copper-gold deposits. Chile
is a globally significant mining jurisdiction being the world's largest
producer and exporter of copper.

 

The Especularita Project is located in the coastal metallogenic belt of Chile
which hosts significant copper mines and deposits, including Teck's Carmen de
Andacollo copper mine, and boasts excellent access to infrastructure such as
roads, power and ports. Significant historical small-scale and artisanal
workings for both copper and gold are readily evident in the exploration
project area. The coastal belt offers deposit type optionality for copper
including porphyry and IOCG style deposits as well as newly recognised
intrusive-related copper and gold deposits.

 

Great Southern Copper is strategically positioned to support the global market
for copper - a critical battery metal in the clean energy transition around
the world. The Company is actively engaged in exploration and evaluation work
programmes targeting both large tonnage, low to medium grade Cu-Au as well as
high-grade Cu-Ag-Au deposits.

 

Further information on the Company is available on the Company's website:
https://gscplc.com (https://gscplc.com)

 

Competent Person Statement

 

The information in this announcement that relates to exploration results is
based on and fairly represents information reviewed or compiled by Mr Sam
Garrett, a Competent Person who is a Member of the Australian Institute of
Geoscientists and a Fellow of the Society of Economic Geologists. Mr Garrett
is the CEO and a shareholder of Great Southern Copper PLC. Mr Garrett has
sufficient experience that is relevant to the styles of mineralisation and
types of deposit under consideration and to the activity being undertaken to
qualify as a Competent Person as defined in the 2012 Edition of the
"Australasian Code for Reporting of Exploration Results, Mineral Resources and
Ore Reserves". Mr Garrett has provided his prior written consent to the
inclusion in this announcement of the matters based on information in the form
and context in which it appears.

 

This announcement includes information that relates to Exploration Results
prepared and first disclosed under the JORC Code (2012) and extracted from the
Company's previous LSE announcements as noted, and the Company's Prospectus
dated 20 December 2021. Copies of these announcements are available from the
LSE Announcements page of the Company's website: www.gscplc.com.

 

The Company confirms that it is not aware of any new information or data that
materially affects the information included within the Prospectus dated 20
December 2021.

 

Forward Looking and Cautionary Statements

Some statements in this announcement regarding estimates or future events are
forward-looking statements. They include indications of, and guidance on,
future earnings, cash flow, costs and financial performance. Forward-looking
statements include, but are not limited to, statements preceded by words such
as "planned", "expected", "projected", "estimated", "may", "scheduled",
"intends", "anticipates", "believes", "potential", "predict", "foresee",
"proposed", "aim", "target", "opportunity", "could", "nominal", "conceptual"
and similar expressions. Forward-looking statements, opinions and estimates
included in this report are based on assumptions and contingencies which are
subject to change without notice, as are statements about market and industry
trends, which are based on interpretations of current market conditions.
Forward-looking statements are provided as a general guide only and should not
be relied on as a guarantee of future performance. Forward-looking statements
may be affected by a range of variables that could cause actual results to
differ from estimated or anticipated results and may cause the Company's
actual performance and financial results in future periods to materially
differ from any projections of future performance or results expressed or
implied by such forward-looking statements. So, there can be no assurance that
actual outcomes will not materially differ from these forward-looking
statements.

 

 

 

 

 

 

 Hole ID           From           To             Interval   Cu       Ag     Sb
                   (m)            (m)            (m)        (%)      (g/t)  (ppm)

 CNG25 DD001       27             47             20         3.31     269.9  934
              inc  31             38             7          5.72     489.6  1085
              inc  35             38             3          6.62     562.7  407

 CNG25 DD002       38.9           43.1           4.2        1.73     126.5  824

 CNG25 DD003       36.6           55.2           18.6       1.85     146.6  798
              inc  39             52             13         2.48     198.1  1049
              inc  48             51             3          3.31     254.7  1608
              inc  50             51             1          4.64     406    2150

 CNG25 DD004       no significant intercept

 CNG25 DD005       35             56             21         2.9      246.7  978
              inc  37             52             15         3.79     328.4  1252
              inc  40             52             12         4.24     369.5  1279
              inc  45             52             7          5.08     449.6  1309
              inc  45             47             2          6.05     547.5  645

 CNG25 DD006       132.54         132.91         0.46       0.08     24.9   5.48

 CNG25 DD007       87             120            33         1.96     60.6
              inc  88             91.85          3.85       5.21     318
              and  115            120            5          5.59     99.2
              inc  116.4          118.9          2.5        9.67     175.4

 CNG25 DD008       0              1.2            1.2        0.512    31.3   28
                   0              31             31                  7.1
              inc  8              22             14                  9.6

 CNG25 DD009       no significant intercept

 CNG25 DD010       no significant intercept

 CNG25 DD011       no significant intercept

 CNG25 DD012       24             27             3          3.43     164.7  39.6

 CNG25 DD013       26.1           39.1           13         1.82     161.5  44.2
              inc  28             33             5          3.04     322.4  23.4

 CNG25 DD014       no significant intercept

 CNG25 DD015       41.15          51.05          9.9        5.47     442.5  685.3
                   43             46             3.0        7.59     612.7  443.4

 CNG25 DD016       89.80          96.50          6.7        4.96     381.1  9.3
                   85.80          87.00          1.2        1.21     76.3   258.0

 CNG25 DD017       76             84.10          8.1        1.76     68.1   269.5
                   71             71.60          0.6        1.11     100.0  7.7

 CNG25 DD018       133.00         135.50         2.5        1.08     101.6  208.5

 CNG25 DD019       99.60          106.80         7.20       1.47     122.3  513.7
              inc  103.5          104.9          1.4        3.75     319.1  341.1

 CNG25 DD020       80.10          88.50          8.40       1.49     121.4  219.8
              inc  80.1           83.3           3.2        2.63     239.7  155.3

 CNG25 DD021       no significant intercept

 CNG25 DD022       no significant intercept

 CNG25 DD023       no significant intercept

 CNG25 DD024       no significant intercept

 CNG25 DD025       28.00          31.00          3.00       0.91     61.7   4
              inc  29             30             1          1.38     88.6   2.2

 CNG25 DD026       7.40           9.30           1.9        0.55     47.9   264.1
                   29.93          30.70          0.77       2.23     92.5   24.0
                   38.00          39.00          1          0.91     26.0   67.1
                   41.50          42.00          0.5        1.09     6.4    80.9
                   66.10          66.84          0.74       1.98     94.1   11.0
                   90.00          92.00          2          0.62     33.1   17.0

 CNG25 DD029       82.30          88.62          6.32       1.39     98.2   2.6
              inc  82.30          82.90          0.6        1.24     76.2   3.8
              and  87.93          88.62          0.69       9.76     716.0  11.8

 CNG25 DD030       35.20          37.35          2.15       0.04     10.2   54.4

 CNG25 DD031       90.40          97.60          7.2        2.58     188.7  550.5
              inc  90.40          92.18          1.78       4.02     271.0  1008.9
              and  96.50          97.60          1.1        8.92     715.3  1430.9
                   110.90         113.05         2.15       2.45     186.4  1425.5
                   120.00         120.95         0.95       0.547    47.1   132.0

 

Table 1: Summary of significant intercepts for Phase I, Phase II and Phase III
GSC drill holes at Cerro Negro Prospect, Chile

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